In the usual honing machine, the honing tool is expanded, that is, the stones of the tool are moved radially outwardly, by turning a shaft which shifts the expanding cams in the tool. When the tool is first inserted into the bore of the work to be honed, the stones are in a radially collapsed position and are initially expanded at a relatively fast rapid traverse rate by a motor which turns the shaft. This continues until just before the stones engage the wall of the bore, at which time the shaft is turned at a slower speed to expand the stones into the work at a reduced rate sometimes referred to as a coarse feed rate. Thereafter, the shaft is turned at a still slower speed to expand the stones at a relatively slow fine feed rate and effect honing of the bore as the stones rotate and reciprocate. When the bore has been honed to a predetermined diameter, an "at-size" signal is automatically produced and effects radial collapse of the stones to enable the tool to be withdrawn from the bore.
As the stones wear, the effective diameter of the tool is reduced. As a result, a tool with worn stones must be expanded through a greater distance from a given starting point than a tool with new stones before the stones engage the wall of the bore. If the tool is expanded from the same starting point at the beginning of each cycle, the intervals of rapid traverse, coarse feed and fine feed will be of improper duration as stonewear occurs.
In order to take stonewear into account, prior honing machines have included electro-mechanical compensators which detect the stonewear and which cause the tool to retract to progressively less collapsed starting points as stonewear occurs. While such compensators do tend to adjust the rapid traverse, coarse feed and fine feed cycles as the stones wear, they are not highly accurate. Moreover, prior electro-mechanical stonewear compensators are structurally complex and require the machine operator to make various mechanical adjustments to reset the compensator each time the stones are replaced.